Traps set west of Portland overflow with Japanese beetles

Traps set in conjunction with an Oregon Department of Agriculture eradication campaign in the Portland area caught a stunning 12,000 Japanese beetles, an invasive pest that can cause major damage to home gardens and to nursery, vegetable, vineyard and orchard crops.

A department official hastened to say the heavy count — only 372 were caught last year and that was enough to trigger the eradication effort — doesn’t mean the campaign didn’t work.

This past spring, department contractors treated the grounds of about 2,400 residences on 1,000 acres west of Portland with a granular form of the insecticide Acelepryn. Adult beetles laying eggs this summer weren’t harmed, but grubs that hatch in the treated areas will ingest the insecticide and die, interrupting the generational cycle. The ag department planned five years of annual treatments, a pattern that has worked in other states.

Clint Burfitt, who is in charge of the treatment program, said the insecticide targets beetles at their most vulnerable life stage but is not hazardous to pets or people.

In a department news release, Burfitt acknowledged the trap count was higher than expected but said the traps are providing good information.

“The good news is that the bulk of the catches are centered in the middle of our treatment zone, so there is a well-defined epicenter for this infestation,” he said in a prepared statement. When the traps are removed this fall, the department will analyze data and plan next year’s eradication work, he said.

Based on past experience, Burfitt expects the number of beetles trapped to decrease 90 percent each year. He predicted the count will drop to more than 1,000 next year, and to single digits by the fifth year.

About 2 percent of the beetles were found in traps set outside the treatment zone, Burfitt speculated that beetles traveled with yard clippings and landscape debris or hitchhiked on vehicles. To counter that, the department, Washington County Solid Waste & Recycling and Metro, the regional government, have asked residents to put grass clippings in curbside containers. Garbage haulers take it to a Hillsboro landfill for deep burial. At the same time, the agencies asked landscaping companies to take debris to a quarantined drop site in the area.